Over the years, I have learned some very good electrical diagnostic routines that have made finding a variety of electrical problems both fun and very fulfilling. I have heard it said that when hunting for electrical problems, there is no right and no wrong way to do the job. I would question, and most likely argue, that point.
The process of electrical problem analysis for me started many years ago with some training, and has continued with much practice and thought about how this process can be made better. Of all the classes I have taken on electrical problem analysis, two classes stick in my mind as great classes. One was a two-hour class done by our local Interstate battery distributor and the white-haired old guy talked about the simplicity of using volt-drop testing when looking for unwanted resistance problems. That was a simple class, but the content of the class has stuck with me over the years. The other class was done by a great electrical trainer, Vince Fischelli. The class was about critical thinking and using the built-in loads on the vehicle (starter, headlights etc.) to load the circuits and actively test for proper circuit operation.
These two trainers captured my attention on electrical testing and from the things I learned from them, I was able to turn “the finding of electrical problems” into a game. So, how do you play the game; what are the rules?
Rules of the game
Many years ago, Mr. Ohm and Mr. Kirchhoff wrote down some really cool stuff about electricity. These laws deal with voltage, resistance and current flow and how they all play together. Once you gain an understanding of these rules (electrical principles), playing the game can be fun.
When I got into this business in 1992, I was told to throw away my conventional test light, since using it on the electrical systems of “today” would kill computer sensors and drivers. Here we are 25 years later, and I have a very good selection of test lights using a variety of bulbs. Do I use them for testing today? You bet I do, although I have learned there is a time and a place for every tool and if these test lights are used in the proper places, they can be great tools.
Admittedly, one of the tools that I have replaced test lights with is the Power Probe. This is a wonderful tool but it, too, can be used in the wrong places. If it is used improperly, computer drivers magically go away. Every tool has its place and knowing the place to use the tools can be a mark of a true craftsman.
When it comes to finding electrical problems, the first piece of information you need is a wiring diagram. We have all heard wiring diagrams called “electrical road maps” and this seems like a good description, since not only does the diagram show you where the electricity flows, but also information like how the circuit is designed and what components are in the circuit are also included in the diagram. Without a wiring diagram, you have no way of knowing which wires power the component or which wires are ground or control wires. These few pieces of information are very crucial to the operation of any electrical component.
If you want to test the powers and grounds in a circuit, you can use a volt meter, a bulb test light, or an LED test light, but stop and consider what you are testing. It doesn’t do much good to use a volt meter to test the voltage on a circuit that is not loaded, since the voltage of a non-grounded circuit will always be system voltage, regardless of the resistance in the circuit. The circuit needs to have a load put on it for the test to be accurate. This will require you to either turn the circuit on, or simulate a load with a bulb test light, or even a variable load tool I built that uses 1157 bulbs. With this tool, I can regulate a load from 2.5 amps through 15 amps. It is sort of like a test light on steroids. With a circuit properly loaded, you can get an accurate voltage and volt drop measurements.
Another valuable piece of equipment needed to make testing of electrical circuits easy is a scan tool that will communicate with the modules on the vehicles and have the capability of bidirectional control of the components. Being able to turn components on and off without having the engine running or the vehicle in operation can be very valuable. Let’s say you are working on an A/C compressor clutch that will not lock up — being able to have the engine off and using the scan tool to activate the clutch while testing the power and ground can be a real time saver.
Last but not least on the list of time savers is having such a simple thing as a package of colored highlighters to identify the different parts of the circuit. Being able to identifying the different parts of the circuit with different colors can make it simple to just glance at a wiring diagram and see which part of the circuit is powered, grounded or switched, or even if there is a different voltage other than vehicle system voltage. All this information can be found in a wiring diagram, if you spend the time to print it out and study it.
In the shop is a nice-looking 2001 Mazda 626 with an overheating problem. The vehicle is powered with a 2.5 V6 engine with automatic transmission. The odometer has recorded 205,000 miles and the vehicle is nice and clean. This is a vehicle I have serviced in my shop for a few years.
|2001 Mazda 626 — Odometer 200,500 miles. Powered with a 2.5 V6 engine with an automatic transmission.|
The vehicle came to the shop with an overheating complaint. When interviewing the person who drives the vehicle, I found the temperature gauge would climb when the vehicle was climbing steep grades. More questioning found the problem to also be after the vehicle was driven for an extended period of time.
Checking the basics, I found the cooling system low on coolant. Any time I see this condition, my thoughts turn to combustion chamber or head gasket leaks or a plugged up radiator. Before I can condemn the engine, I first need to check for any external coolant leaks. If there are external leaks, they need to be fixed and then the engine tested for combustion leaks.
Pressure testing the cooling system revealed a heater hose with a pinhole leak that was loosing coolant. This repair was simple, with just a piece of heater hose. The other coolant hoses were inspected with no problems found.
Being thorough with testing problems like this is very important, since there are several things that can cause an overheat problem. The low coolant is a sure bet to cause an overheating problem, but is there more? Is the leaking hose a symptom of another problem, or is it the cause of the problem?